This invention relates to lubricating resin compositions and seal rings and other sealing members formed of the same.
Sealing members such as seal rings are used in hydraulic devices cooperating with an automatic speed change gear such as a non-stage transmission. According to the use environment, a seal member made mainly of cast iron or a synthetic resin is selectively used. It is required that such seal members be high in oil sealability, low in friction, high in wear resistance, less likely to damage a mating metallic member, and easy to handle in fitting on a shaft.
Among conventional seal members, those made of cast iron have passable wear resistance but are low in sealing properties. Thus, a hydraulic unit in which are used cast iron seals requires a large-sized oil pump to compensate for oil leak through the seals. Cast iron seals are higher in elastic modulus and lower in toughness than synthetic resin seals. Thus it is difficult to fit a seal member made of cast iron on e.g. a shaft. This is especially true for an oil seal ring, a kind of seal member which is typically split by a slit at one point of its circumference. Such an oil seal ring made of cast iron and having an outer diameter of 20 mm or under tends to break when it is deformed to widen the slit to fit the ring on a shaft.
On the other hand, synthetic resins such as tetrafluoroethylene, polyamide, polyphenylene sulfide, aromatic thermoplastic polyimide, and aromatic polyether ketone are lower in elastic modulus than cast iron. Thus, a seal ring molded of such a resin and various fillers is less likely to snap when deformed to widen the slit. It is also high in sealability.
Among such synthetic resins, tetrafluoroethylene resin is especially low in elastic modulus, high in sealability and low in friction. Thus, many conventional seal members are made mainly of this resin with various fillers added to improve wear resistance and creep resistance.
However, such a seal ring has one drawback that if brought into frictional contact with a mating member at high speed in a high-temperature environment, typically at 100xc2x0 C. or over, wear tends to progress quickly even before the surface pressure reaches 1 MPa. Compressive creeping is also high. Thus, in such an environment, this type of seal ring cannot maintain high sealability.
A seal member made of polyamide or polyphenylele sulfide resin tends to melt and thus wear severely if brought into frictional contact with a mating member at high speed in a high-temperature atmosphere. Thus, if such seal members are used as oil seals, oil leak can occur.
A seal member made of an aromatic thermoplastic polyimide resin is high in heat resistance but low in toughness. Thus a seal ring having a slit and made of this resin is difficult to widen the slit. It is not wear-resistant either.
A seal member made of an aromatic polyether ketone resin has a moderate elasticity and a sufficient toughness, so that it can be easily fitted on e.g. a shaft. It also maintains low friction and high wear resistance when brought into frictional contact with a mating member at high speed even in a high-temperature atmosphere of 100xc2x0 C. or over.
According to the type of mating metallic member, different kinds of fillers are added to seal members made of aromatic polyether ketone resin. Typical such-fillers include glass fiber, carbon fiber, potassium titanate whisker, graphite, mica, talc and tetrafluoroethylene resin.
Of these fillers, fibrous fillers such as glass fiber, carbon fiber, and potassium titanate whisker, and flaky fillers such as graphite, mica, and talc are used to improve mechanical properties and wear resistance. Solid lubricant such as tetrafluoroethylene, graphite, and molybdenum disulfide are used to improve frictional properties.
But seal rings containing such fillers have a drawback that it is difficult to widen the slit and thus to mount the ring on e.g. a shaft. The degree of difficulty in widening the slit depends on the kind and amount of fillers used. For example, it is especially difficult to widen the slit of a seal ring containing a large amount of flaky fillers such as graphite, mica or talc. Thus, for a small seal ring of synthetic resin having an outer diameter of 20 mm or under, it has been difficult to meet all the requirements, i.e. low friction, wear resistance and ease of mounting.
A seal member containing both carbon fiber and a solid lubricant has passable fritional/wear properties (Japanese patent publications 61-58093 and 9-142487). But such a seal ring containing both of them and having an outer diameter of 20 mm or under tends to be low in wear resistance and sealability if the filler contents are reduced so that the slit can be widened easily. If such a seal member is used with a mating member made of an aluminum alloy, the carbon fiber in the seal ring tends to damage the soft mating member. The damaged mating member in turn causes abnormal wear of the seal ring.
In Japanese patent publications 1-29379 and 2-175793, seal members containing both potassium titanate whisker and a solid lubricant are disclosed. If such seals are brought into frictional contact with a mating member at high speed at high temperature, typically 100xc2x0 C. or over, the reinforcing effect of the potassium titanate whisker tends to be insufficient, thus increasing the amount of wear. Further, if these seals are brought into frictional contact with a mating member made of an aluminum alloy, the former tends to damage the latter. This leads to reduced sealability.
In order to prevent damage to a mating member made of an aluminum alloy, seal members containing a particulate or flaky filler or a solid lubricant were proposed in Japanese patent publications 8-159292 and 10-53700. But they still have insufficient wear resistance and tend to damage a mating member.
Even a seal member containing carbon fiber, a particulate or flaky filler and a solid lubricant still damages an aluminum alloy mating member. One way to reduce attack to the aluminum alloy mating member is to add a large amount of flaky fillers. But this makes it increasingly difficult to widen the slit of a seal ring and amount it.
For a hydraulic unit in which are mounted seals such as seal rings, compactness and high performance are required. It is also required to operate reliably under high pressure. For compactness of the entire unit, seal rings also have to be as small in outer diameter as possible. It is also required that their slits can be easily widened.
Conventional seal rings made of an aromatic polyether ketone resin are low in sealbility when brought into frictional contact with a mating member at high speed at high temperature of 100xc2x0 C. or over.
If the filler content in a seal ring having an outer diameter of 20 mm or under is reduced so that its slit can be more easily opened, the degree of wear tends to increase.
The larger the bending strain of the resin composition forming a seal ring, the more easily the seal ring can be fitted on a shaft.
The shaft or cylinder is usually formed from aluminum alloy for greater machinability and light weight. If a seal is mounted on a hydraulic cylinder or a piston, such a mating member made of aluminum alloy in frictional contact in lubricating oil is more liable to wear than when operating in a dry state with no lubricating oil.
This is because lubricating oil is not sufficiently supplied to the sliding surface under high-speed and high-surface pressure condition and because if a thin oil film is formed on the sliding surface, the transition of a lubricating material from an aromatic polyether ketone resin composition to the mating member does not occur. Thus neither solid or liquid lubricant is supplied to the sliding surface, so that the wear of the mating member results.
An object of the invention is to provide a lubricating resin composition that is high in wear resistance and sealability and less likely to wear or otherwise damage an aluminum alloy mating member even under insufficient supply of lubricating oil.
Another object of the present invention is to provide a lubricating resin composition that maintains high wear resistance and sealability when brought into frictional contact with a mating member at high speed at high temperature of 100xc2x0 C. or over and that is less likely to damage an aluminum alloy mating member even when brought into frictional contact with the mating member at a surface pressure of 1 MPa or over.
Another object of the present invention is to provide a seal ring that is high in wear resistance and sealability and less likely to damage an aluminum alloy mating member, and particularly a seal ring having an outer diameter of 20 mm or under and having a slit which can be opened easily for easy mounting on a shaft.
According to the invention, there is provided a lubricating resin composition comprising 50-90 vol % of an aromatic polyether ketone resin, 5-30 vol % of an aromatic polyamide fiber, and 2-30 vol % of tetrafluoroethylene resin. The lubricating resin composition may be used as a seal.
By adding both an aromatic polyamide fiber as a reinforcing material and a tetrafluoroethylene resin as a lubricant in a resin composition containing an aromatic polyetherketone resin as a main component, both the wear resistance and frictional properties of the composition improve. Sealability thus improves. The specific amount of aromatic polyamide fiber improves the wear resistance of a seal made from the resin composition. Such a seal would not wear or damage an aluminum alloy mating member.
The composition according to the invention may further comprise 2-20 vol % of mica or talc, 2-30 vol % of whisker having a Mohs hardness of 3 or under, or 2-30 vol % of a particulate inorganic compound having a Mohs hardness of 3 or under.
By using both an aromatic polyamide fiber as a reinforcing material and mica or talc and whisker or particulate inorganic compound having the specific hardness, the aromatic polyamide fiber macroscopically reinforces the entire polyether ketone resin, while the mica or talc, or the whisker or particulate inorganic compound having the specific hardness microscopically reinforce the aromatic polyamide fiber.
By adding these reinforcing materials in specific amounts, they synergistically improve the wear resistance of the composition while compensating for their weak points. Thus, sealability and low attack to an aluminum alloy mating member required for the resin composition improve.
From another aspect of the invention, there is provided a seal ring formed from the lubricating resin composition and having a slit. The seal ring may have an outer diameter not exceeding 20 mm and having a bending strain (under ASTM D790) of 3% or over.
Made from such a resin composition, practically all the properties required for the seal ring improve. The use of the specific reinforcing materials improve bending elasticity of the ring. By forming a seal ring from the resin composition having a bending strain (ASTM D790) of 3% or over, its slit can be widened easily even if its outer diameter is 20 mm or under.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: